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| United States Patent |
5,217,807
|
|
Steiber
, et al.
|
June 8, 1993
|
Metal acrylates as rubber-to-metal adhesion promoters
Abstract
This invention relates to the improvement of rubber-to-metal adhesion and
adhesion retention in sulfur vulcanizable, metal reinforced rubber
compositions via the use of metal acrylate and/or methacrylate adhesion
promoters.
| Inventors:
|
Steiber; Joseph F. (Prospect, CT);
Hong; Sung W. (Cheshire, CT);
Seibert; Rebecca F. (Waterbury, CT)
|
| Assignee:
|
Uniroyal Chemical Company, Inc. (Middlebury, CT)
|
| Appl. No.:
|
625793 |
| Filed:
|
December 11, 1990 |
| Current U.S. Class: |
428/378; 525/274; 525/349 |
| Intern'l Class: |
C08J 005/04 |
| Field of Search: |
525/274,245,261,262,301,236,237,194,195
428/378
|
References Cited
U.S. Patent Documents
| 4259218 | Mar., 1981 | Haws | 525/236.
|
| 4720526 | Jan., 1988 | Roland | 525/273.
|
| 4756353 | Jul., 1988 | Nordsiek | 525/236.
|
| Foreign Patent Documents |
| 2368515 | May., 1978 | EP.
| |
| 0039769 | Nov., 1981 | EP.
| |
| 0056156 | Jul., 1982 | EP.
| |
| 3737595 | May., 1988 | EP.
| |
| 49-15947 | Apr., 1974 | JP.
| |
| 50-154386 | Dec., 1975 | JP.
| |
| 58-23866 | Feb., 1983 | JP.
| |
| 286770 | Jun., 1986 | JP.
| |
| 273017 | Nov., 1986 | JP.
| |
Other References
Chemical Abstracts, vol. 109, Nov. 28, 1988, p. 81, Abstract 191991a, and
JP, A, 63139970 (Bridgestone Corp.) Jun. 11, 1988.
Abstract-T900,003, Method of Improving Rubber to Brass Adhesion (R. L.
Arnold et al) Jul. 18, 1972.
USSR Patent 1,397,461 (23 May 88) English Abstract.
|
Primary Examiner: Henderson; Christopher
Attorney, Agent or Firm: Thompson; Raymond D.
Parent Case Text
This is a continuation of application Ser. No. 07/297,900 filed Jan. 17,
1989, now abandoned.
Claims
What is claimed is:
1. A reinforced elastomeric composition produced by curing a brass coated
metal reinforcement in intimate contact with a blend of:
a) vulcanizable rubber;
b) from about 0.2 to about 10.0 parts of sulfur per 100 parts by weight of
rubber; and
c) from about 0.1 to about 5.0 parts of sulfur cure accelerator per 100
parts by weight rubber, wherein the sulfur cure accelerator is selected
from the group consisting of a benzylthiazole sulfenamide,
2-mercaptobenzothiazole or benzylthiazyl disulfide; and
d) from about 0.05 to about 20 parts of a diacrylate or dimethacrylate salt
of aluminum, zinc or magnesium per hundred parts by weight of rubber.
2. A reinforced elastomeric composition of claim 1 further comprising:
from about 0.05 to about 20 parts of at least one bonding agent selected
from the group consisting of cobalt salt,
2,3,5,6-tetrachloro-1,4-benzoquinone, a formaldehyde donor and a
resorcinol donor.
3. A reinforced elastomeric composition of claim 1 wherein the vulcanizable
rubber is selected from the group consisting of natural rubber, synthetic
rubber, and blends thereof.
Description
TECHNICAL FIELD
The present invention is directed toward improving the adhesion and
adhesion retention between rubber compositions, such as those used in the
manufacture of tires, conveyor belts, hoses and the like and brass coated
wire or cable which is embedded in the stock.
The improved useful life of modern rubber compositions, especially in
belting and tire end uses via more sophisticated and effective
antiozonant/antioxidant packages have necessitated the desirability of
adding materials to the rubber compositions to improve useful article life
and service through increased reinforcing agent adhesion and adhesion
retention. Improved adhesion between rubber and brass coated wire is
obtained according to the present invention.
BACKGROUND ART
It is often desirable to reinforce rubber articles by incorporating therein
metal reinforcing elements. For example, tires, conveyor belts, power
transmission belts, timing belts, hoses and a variety of other rubber
articles are often reinforced with metal wire. In order for rubber
articles which are provided with steel reinforcing elements to function
effectively, it is important that good adhesion between the rubber and the
metal reinforcing elements be maintained. One of the most common methods
of enhancing the adhesion of wire filaments to rubber is to coat the
filament with another material, for example, pneumatic vehicle tires are
often reinforced with cords prepared from steel filaments which are coated
with brass. Normally, steel reinforcing elements are coated with a brass
that is an alloy of copper and zinc. However, ternary brass alloys that
are useful for coating steel reinforcing elements are also known by those
skilled in the art. For example, U.S. Pat. No. 4,347,290 discloses a
ternary brass alloy which contains copper, zinc and cobalt. These and
other ternary alloys, such as those containing copper, zinc and iron or
tin are known to be effective in improving rubber to metal adhesion.
It is also known that various agents can be mixed into the rubber which
will increase adhesion between the rubber and metal reinforcements
imbedded in it. U.S. Pat. No. 3,894,903 discloses a process for improving
the bonding of rubber to copper and copper alloys by incorporating into
the rubber before vulcanization certain triazines, for example
2-N-hydroxyphenoxy-4-chloro-6-aminotriazine.
U.S. Pat. Nos. 3,991,130 and 3,905,947 disclose a method for improving
adhesion between vulcanizable elastomeric compositions and metal surfaces
by incorporating into the elastomer an organo-nickel salt and then
subsequently vulcanizing the elastomeric composition while it is in
contact with the metal surface.
U.S. Pat. No. 4,521,558 improves rubber adhesion to metal via the use of
allyl phosphite and phosphate esters and various iminodiacetic acids and
salts.
Cobalt complexes such as cobalt-mercaptobenzothiazole complexes as
disclosed in UK Patent No. 914,787 have been used in natural and synthetic
rubbers both as accelerators and to permit the rubber to be bonded more
effectively to ferrous metals during vulcanization.
Acrylates have been added to various non-crosslinkable synthetic resin
systems to improve adhesion to certain metals. For example, calcium
acrylate was added to polyvinylchloride in Japan Kokai 52/3633 (Jan. 12,
1977) to improve the resin adhesion to soft steel sheet. Japan Kokai
50/77486 (Jun. 24, 1975) discloses the use of aluminum, zinc and/or
calcium acrylates in non-curing PVC compositions to yield improved peel
strengths with zinc wire. Polyolefin hot melt adhesives for aluminum were
taught in Japanese Kokai 51/4223 (Jan. 14, 1976) to have bonding peel
strength increased via the addition of zinc acrylate to the adhesive
composition.
Metal diacrylates are known to function as cross-linking agents for rubbery
material in the presence of various peroxide initiator systems. For
example, Japanese Kokai 50/154386 (Dec. 12, 1975) discloses that adhesion
to zinc-plated iron is good with EPDM/peroxide/carbon black compositions
containing aluminum, zinc and/or calcium acrylate.
Similar results are taught in Japanese Patent 49/15947 (Apr. 18, 1974)
which discloses a steel bonding composition containing rubber, a peroxide,
carbon black and glycidyl methacrylate.
A two part liquid adhesive for steel plates is described in Japanese Kokai
58/23866 (Feb. 12, 1983) as containing an elastomer, a peroxide, an alkali
metal and acrylic monomer.
Acrylates, at levels useful for promoting rubber adhesion to metal are not
known to contribute to rubber crosslinking when sulfur curing systems are
used.
Peroxide initiated curing systems for rubbery materials have proven to be
unsatisfactory in the production of finished articles that are required to
have extended flex life, for peroxide cured rubbers tend to crack when
subject to repeated flexing. Additionally, peroxide curing systems tend to
be expensive and because of their reactivity, they require careful
handling to avoid the creation of a dangerous environment.
As a result, many industries, such as the tire and industrial belting
industries prefer to use sulfur cure vulcanization systems for
cross-linking rubber.
SUMMARY OF THE INVENTION
This invention reveals the use of metal acrylates in sulfur curable
rubber-metal composites to increase the adhesion and adhesion retention
between the metal and the rubber composition. Furthermore, most of the
metal acrylates of this invention do not negatively effect the processing
or cured properties of the systems as is often the case with previous
adhesion promoters. As a result of the retention of the inherently
desirable properties of the system, the composites are useful in finished
goods requiring long life, such as tires or industrial belting.
More specifically, this invention discloses a composite comprising a sulfur
curable rubber composition with brass coated metal wire embedded therein
wherein said rubber composition contains from about 0.05 to about 20 parts
per hundred parts of rubber of at least one adhesion promoter selected
from acrylate and methacrylate salts of di- and tri-valent metals.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to sulfur curable rubber compositions reinforced
with brass coated metal wherein the composition contains certain metal
acrylate adhesion promoters and composite articles made therefrom.
The rubber in the composites of this invention can be selected from a wide
variety of rubbery polymers for the instant adhesion promoters are
effective in both natural and synthetic rubbers that are sulfur curable.
Some representative examples of rubbers commonly used in the composites of
this invention include natural rubber, styrene-butadiene rubber, synthetic
polyisoprene, polychloroprene, cyclene rubbers, polybutadiene, nitrile
rubbers, carboxylated nitrile rubbers, butyl rubbers, EPDM
(ethylene-propylene-diene) rubbers, epichlorohydrin homo and copolymers,
EPR (ethylene-propylene) rubbers, polyisobutylene, norbornene rubbers,
thiokol rubbers, and blends of various combinations of these and other
diene rubbers.
The curative systems employed in the cross-linking of the compositions of
this invention comprise sulfur and/or a sulfur donor compound and
preferably, at least one sulfur cure accelerator.
The sulfur donor compounds which may be employed in conjunction with or in
the alternative to sulfur are well known to those skilled in the art of
rubber compounding. Illustrative of such sulfur donor compounds are
2-(4-morpholinyldithio)benzothiazole, 4,4-dithiodimorpholine,
N,N'-caprolactam disulfide and the like.
The sulfur cure accelerators which may be employed include thioureas, such
as N,N'-dibutylthiourea, 2-mercaptoimidazoline, tetramethylthiourea and
the like; guanidine derivatives, such as N,N'-diphenylguanidine and the
like; heterocyclics, such as mercaptobenzimidazole, mercaptobenzthiazole,
2,2'-dibenzothiazyl disulfide, zinc 2-mercaptobenzothiazole and the like;
and sulfenamides, such as N-oxydiethylene-2-benzothiazolesulfenamide,
N-t-butylbenzothiazylsulfenamide, N-cyclohexyl-2-benzothiazylsulfenamide,
N,N-diisopropyl-2-benzothiazylsulfenamide and the like. Moreover, mixtures
of two or more sulfur cure accelerators may be employed in the curing
agent of this invention. The preferred accelerators are thiazoles and
sulfenamides, with sulfenamides being particularly preferred.
The sulfur cure accelerator is generally present in amounts of between
about 0.1 parts and about 5 parts per 100 parts of rubber, with preferably
between about 0.3 part and about 3.0 parts of accelerator per 100 parts of
rubber being present. Most preferably, between about 0.3 parts and about
2.0 parts of accelerator per 100 parts of rubber are employed.
Generally, between about 0.2 and about 10, preferably between about 3.0 and
about 8.0 parts of sulfur per hundred parts of rubber are employed.
Many terms are used to describe the metal reinforcing elements used to
strengthen rubber articles. The terms "cord", "tire cord", "cable",
"strand", "wire", "rod", "plate", and "filament" can all be used to
describe metal reinforcing elements used to strengthen rubber articles.
The term "metal reinforcement" as used herein is devised to be generic to
all articles for reinforcing rubber articles including those listed above.
Thus, without being limited thereto, a metal reinforcement can be a metal
wire, metal cord, a metal tire cord, a metal cable, a metal strand a metal
rod, a metal plate or a metal filament.
The metal reinforcement elements which are generally preferred for use in
this invention are brass plated steel.
Metal wires used in the tire industry are manufactured by cold drawing high
carbon steel and subsequently brass plating same. The brass plating not
only enhances the adhesion of the wire cord to rubber but also facilitates
drawing the wire to a fine diameter of about 0.20 mm. The wire filaments
are combined to form a strand and several strands combined to obtain the
final tire cord.
The adhesion promoters of this invention are the acrylate and methacrylate
salts of di- and tri-valent metals. Preferred are the aluminum, zinc and
magnesium acrylate and methacrylate salts either alone or in combination
with various commercially available bonding agents such as the cobalt
salts, e.g., cobalt stearate which is widely used in the tire industry;
2,3,5,6-tetrachloro-1,4-benzoquinone (sold by Uniroyal Chemical under the
trademark VULKLOR); and various formaldehyde and resorcinol donors well
known to the art.
The adhesion promoters of this invention can be mixed into a rubber using
ordinary compounding techniques. Generally, it will be convenient to mix
the adhesion promoter into the rubber composition of this invention
simultaneously with other desired compounding ingredients using any
suitable mixing equipment known to those skilled in the art, such as an
internal mixer or mill. Normally, the rubber compositions used in the
composites of this invention will be compounded with sulfur and carbon
black. Numerous mineral fillers, such as clay and silica are commonly used
a partial or total replacements for carbon black. The rubber compositions
of this invention will also commonly contain cure accelerators, scorch
inhibitors, antidegradents, pigments, and processing oils.
The essence of the present invention also finds utility in, for example,
other rubber articles bonded to brass or brass-plated steel such as motor
mounts, cutless bearings, springs, power belts, printing rolls, metal wire
reinforced or braided hose, and wherever it is desired to secure rubber to
metal or provide a flexible and strong, thermally stable bond between
same.
The rubber articles of this invention can be produced by following a
procedure which comprises: 1) preparing a rubber composition which
contains at least one adhesion promoter of this invention, 2) surrounding
the metal reinforcement with the rubber to conform to the desired shape of
the rubber article being produced, and 3) curing (vulcanizing) the rubber
article. Vulcanization of the blends may be carried out in a press, an
oven, or other suitable means until cross-linking has occurred to a
satisfactory state of cure.
Thus, standard techniques well-known to those skilled in the art for
manufacturing rubber articles with metal reinforcing elements embedded
therein can be employed in this invention. In other words, metal
reinforcements can be incorporated into the rubber articles of this
invention using the same techniques that are employed in incorporating
metal reinforcements into ordinary rubber articles. Generally, reinforcing
elements are simply surrounded by uncured rubber containing an adhesion
promoter of this invention in a mold and vulcanized to produce the desired
rubber article which has the metal reinforcement embedded therein.
In the practice of this invention generally from about 0.05 to about 20
parts per hundred parts of rubber by weight (phr) of the adhesion promoter
will be employed in the rubber composition. It is generally preferred for
0.1 to 10 parts of adhesion promoter to be employed in the rubber
composition per hundred parts of rubber by weight. It is more preferred
for 0.5 to 6 phr of an adhesion promoter to be employed in the rubber
composition. It should be noted that various blends of different adhesion
promoters can be employed in the rubber compositions of this invention.
The adhesion promoters described herein can be distributed (mixed)
throughout a rubber using any convenient, technique known to those skilled
in the art. The rubber compositions of this invention are also cured using
standard techniques well known to those skilled in the art. Generally,
such rubber compositions are cured (vulcanized) under pressure at a
temperature ranging from about 100.degree. C. to about 233.degree. C. with
a metal reinforcement being embedded in the rubber composition so as to
form a composite article. It is generally preferred for such composite
articles to be cured at a temperature ranging from 100.degree. C. to
205.degree. C.
The practice of the present invention has been observed to result in
improved aged rubber-metal adhesion, in many cases with improved initial
(original) adhesion. The following examples are included to further
illustrate the rubber-metal composites within the scope of this invention
and to compare them with other rubber-metal composites outside of its
scope. Such comparisons clearly show the superior adhesion retention
obtained by practicing the present invention. The following examples are
merely for the purpose of illustration and are not to be regarded as
limiting the scope of the invention or the manner in which it can be
practiced. Unless specifically indicated otherwise, all parts and
percentages are given by weight.
EXAMPLES
All of the following examples utilize a Masterbatch of the following
recipe:
______________________________________
Parts by Weight
______________________________________
Rubber
Natural Rubber (SMR 5CV)
80.00
Polybutadiene 20.00
Carbon Black 55.00
Zinc Oxide 10.00
Stearic Acid 1.50
Aromatic Oil 7.00
Tackifier Resin 2.00
Diphenylamine/Acetone Reaction Product
1.50
Antioxidant
N-phenyl-N'-(1,3-dimethylbutyl)-p-
1.00
phenylenediamine Antiozonant
Total 178.00
______________________________________
The Masterbatch is prepared by mixing the rubber in an internal mixer and
after one minute adding the zinc oxide and one-half of the carbon black.
After three minutes, the balance of the ingredients is added. The unit is
"swept-down" at five minutes and the material discharged at seven minutes
at from about 122.degree. C. to about 150.degree. C.
Two such batches as described above are prepared and milled together to
realize the final Masterbatch.
Examples A through V are prepared from the following recipe:
______________________________________
Parts by Weight
______________________________________
Masterbatch 178.00
Acrylate (as indicated)
Additional Adhesion Promoters (as indicated)
N-oxydiethylene-2-benzothiazole-
0.70
sulfenamide Accelerator
N-(cyclohexylthio)-phthalimide
0.10
Retarder
Insoluble Sulfur Vulcanizer
5.00
(80% Oiled Crystex, a
Trademark of Stauffer Chemical Co.)
______________________________________
One half of the Masterbatch, the above powders and the balance of the
Masterbatch are added sequentially to an internal mixer and subsequently
discharged at 100.degree. C. Each example is then mill blended for five
minutes.
Samples of each of the composition examples, which are similar to
commercial tire breaker compositions were cured for 25 minutes at
160.degree. C. Other samples were cured for 10 minutes at 177.degree. C.;
the higher temperature cures simulating the "fast cures" favored by the
tire industry. Unaged Physical Properties, i.e., Tensile Strength, 300%
Modulus, % Elongation, Shore A Hardness and Tear (Die C) were determined
on these samples at room temperature and, except for the Shore A Hardness,
at 121.degree. C.
The "Adhesion To Steel Cord" test was conducted according to ASTM D-2229
with pounds to pull-out measured at 121.degree. C. The adhesion pads were
cured for a) 50 minutes at 160.degree. C. or b) 20 minutes at 177.degree.
C. as indicated using 2.times.2 brass coated steel wire.
Tables I and II give the amounts of the various acrylates of this invention
that are present in the samples and the additional bonding agents, if any.
Unaged Physical Properties at room temperature and at 121.degree. C. are
presented.
The wire adhesion data for each example shows the force in pounds necessary
to pull or remove the brass coated steel reinforcing wire from the
vulcanized pad. This "pull-out" force is followed (in the aged and/or
steamed samples) by the percentage of original force retained. Finally,
the amount of rubber remaining on the wire was determined by visual
examination and has been reported as percent retained rubber coverage,
wherein 5 represents 100% coverage; 2 represents 40% coverage; etc.
The rubber coverage measurement is significant in that it visually
represents the adhesion of the rubber composition to the brass plated
steel cord. As is well known to those skilled in the art, the amount of
rubber adhering to the steel cord after it has been pulled from a cured
adhesion pad represents the relationship of the adhesive force attaching
the rubber composition to the surface of the steel cord and the tear
strength of the rubber composition itself. Large percentages of rubber
coverage indicate that the adhesion to the steel cord exceeds the internal
strength of the rubber composition itself, i.e., tear strength. Therefore,
when the rubber coverage is very high it can be concluded that the metal
to rubber adhesion is greater than the force measured to pull the steel
cord out of the rubber pad since the force measured was a result of the
rubber composition rupturing and not the metal to rubber interface.
Normal or unaged testing is merely a measurement of the initial adhesion
properties between the rubber composition and the metallic reinforcement.
Steam aging is an accelerated humidity aging test and is significant in
determining the chemical stability of the chemical bonds formed between
the rubber and the metallic reinforcement when exposed to moisture or
steam.
TABLE I
______________________________________
A B C D E F
______________________________________
Aluminum Dimethacrylate 2.0
Aluminum Diacrylate 2.0
Zinc Dimethacrylate 2.0
Magnesium Diacrylate 2.0
Bonding Agent R-6 2.0
Resorcinol Donor
Vulklor (2,3,5,6-tetrachloro- 1.0
1,4-benzoquinone)
Wire Adhesion lbs. pull/in @ 250.degree. F.
Cured 20' @ 350.degree. F. (177.degree. C.)
Unaged 73 90 67 78 61 89
Aged 2 weeks @ 158.degree. F.
45 69 72 52 50 50
% Retention 64 77 104 67 82 56
______________________________________
TABLE II
RECIPE PHR A B C D E F G H I J K L M N
SMR 5CV 80.00 POLYBUTADIENE 1203 20.00 Z A Z A Z A Z A Z
A Z A V C CARBON BLACK N-351 55.00 N L N L N L N L N L N L U O ZINC
OXIDE 10.00 D D D D D D D D D D D D L N STEARIC ACID 1.50 A A M M A A M
M A A M M K T AROMATIC OIL 7.00 A A A A A A L R TACKIFIER RESIN
2.00 O O DIPHENYLAMINE/ACETONE 1.00 R L
REACTION PRODUCT ANTIOXIDANT * 0.10 ** 0.70 80% OILED CRYSTEX 5.00
*** as indicated 0.10 0.10 0.10 0.10 -- -- -- -- -- -- -- -- -- --
BONDING AGENT R-6 as indicated -- -- -- -- 2.00 2.00 2.00 2.00 -- -- --
-- 2.00 -- SRF 1588A RESIN as indicated -- -- -- -- -- -- -- -- 2.00
2.00 2.00 2.00 -- 2.00 **** as indicated -- -- -- -- -- -- -- -- 1.00
1.00 1.00 1.00 -- 1.00 COBALT STEARATE as indicated -- -- -- -- -- -- --
-- -- -- -- -- -- 2.00 VULKLOR as indicated -- -- -- -- -- -- -- -- --
-- -- -- 1.00 -- METAL DIACRYLATE as indicated 2.00 2.00 2.00 2.00 2.00
2.00 2.00 2.00 2.00 2.00 2.00 2.00 -- -- MOONEY SCORCH, MS @ 270.degree.
F. 17'15" 17'0" 19'0" 17'0" 15'0" 14'45" 15'0" 14'15" 13'30" 13'45"
14'45" 13'30" 14'15" 13'45" PHYSICAL PROPERTIES - Cured 25 Minutes @
320.degree. F. UNAGED Tensile Strength 3470 3290 3350 3260 3160 3100
3300 3090 3100 3020 3160 3200 3180 3060 300% Modulus 1790 1810 2450 2010
1910 1720 2450 1890 1770 1590 2010 1820 2040 2110 Elongation 510 470
400 440 450 480 420 450 500 500 460 510 440 440 UNAGED @
250.degree. F. (121.degree. C.) Tensile Strength 1810 1820 1660 1780
1680 1620 1770 1710 1780 1640 1640 1540 1630 1490 300% Modulus 1080 1070
1450 1280 1170 1020 1220 1090 1220 1080 1430 1200 1430 1340 Elongation
410 450 320 360 360 410 380 410 410 410 310 330 320 310
WIRE ADHESION TESTING - lbs. pull/inch 90* 84 90* 76 90* 80
90* 77 90* 90* 84 89 90* 90* @ 250.degree. F. UNAGED
Coverage -- 5 -- 4 -- 5 -- 4 -- -- 5 4 -- -- AGED 1 DAY IN
STEAM @ 100.degree. C. (212.degree. F.) 48 49 45 39 52 40 46 42
38 50 52 57 37 21 % Retention 53 58 50 51 58 50 51 55 42
56 62 67 41 23 Coverage 4 5 3 3 4 5 4 3 2 4 4
3 3 1 AGED 3 DAYS IN STEAM @ 100.degree. C. (212.degree. F.) 30
36 27 37 34 32 38 30 27 40 35 42 24 14 % Retention 33 43
30 49 38 40 42 39 30 44 42 47 27 16 Coverage 3 2 0 2
2 3 2 1 1 3 3 3 1
*N-PHENYL-N'-(1,3-DIMETHYLBUTYL)-P-PHENYLENEDIAMINE
**NOXYDIETHYLENE-2-BENZOTHIAZOLE SULFENAMIDE ACCELERATOR
***N(CYCLOHEXYLTHIO)-PHTHALIMIDE RETARDER
****NITROMETHYL PROPANOL
ALDA: Aluminum diacrylate
ALDMA: Aluminum dimethacrylate
ZNDA: Zinc diacrylate
ZNDMA: Zinc dimethacrylate
NOTE
UNAGED WIRE ADHESION RESULTS: If three or more wires failed before the
adhesion failed, result recorded is 90*. This is based upon the tensile
strength of the wire. % retention was then based on 90 lbs. pull/inch.
Other unaged data was based on an average of three numbers.
In Table I, the percent retention of adhesion data after two weeks oven
aging at 158.degree. F. (70.degree. C.) shows that compositions containing
the acrylate or methacrylate salt of di- or tri-valent metal provide
outstandingly improved adhesion over that provided by Example A which does
not contain any promoter or by Example F, a commercially used system of
Vulklor and a resorcinol donor combination.
In Table II, the percent of adhesion retention data (after one and three
days steam agings at 100.degree. C.) of examples A through D inclusive
which use the acrylates of this invention as the sole adhesion promoter
versus the composition of examples M and N, which are commercially
utilized adhesion promoter systems, illustrates the superior adhesion
results unexpectedly realized via the use of the metal acrylates of this
invention in sulfur vulcanized rubber compositions. At the same time, the
Unaged Physical Properties of the composition are essentially unaffected.
Bonding Agent R-6 and SRF 1588A resin are resorcinol donors. As the percent
of adhesion data after three days steam aging at 100.degree. C. clearly
indicates, compositions containing a metal acrylate of this invention in
combination with resorcinol/formaldehyde donor systems, i.e. SRF 1588A
Resin and NMP (Examples E through L inclusive), provide outstandingly
improved adhesion over that achieved with the commercially utilized
adhesion promoter cobalt stearate in identical combinations or the Vulklor
and resorcinol donor combination (Examples M and N), again with the unaged
physical properties essentially unaffected.
In summary, it is well-known that acrylates can be grafted to unsaturated
rubber using peroxide systems. Furthermore, unsaturated rubbers can be
cured using acrylate/peroxide cure systems. The instant invention relates
to sulfur and accelerated sulfur cure systems. With these sulfur cure
systems, acrylate salts at the levels useful for promoting adhesion to
metal have little or no effect on the curing of the rubber composition nor
on the cured properties of unreinforced compositions. Therefore, the
superior adhesion brought about by the metal acrylates of this invention
is unexpected.
In conclusion, it is to be understood that all methods and rubber compounds
disclosed herein fall within the scope of the claimed invention and that
the subject invention is not to be limited by the examples set forth
herein. As will be apparent to those skilled in the art, the formulation
of the rubber composition can be varied within the scope of the total
specification disclosure by selection of various rubbers of the type set
forth herein as well as the amounts thereof, and of the acrylate adhesion
promoters and it is believed that practice of the present invention can be
determined without departing from the spirit of the invention herein
disclosed and described, the scope of the invention being limited solely
by the scope of the attached claims.
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